The M4 motorway has not opened today as planned and may not even be ready by Monday – the busiest day for Olympic arrivals at Heathrow.

The chief executive of the Highways Agency, Graham Dalton, today admitted there was 'no guarantee' that the Monday deadline would be met.

'This is some delicate work. We have confidence we will get it done, but a guarantee? I would be kidding you,' he said.

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Good news: The M4 motorway has reopened in both directions a week after it was closed for emergency repair works, the Highways Agency said this morning

'There was only one decision on this because of the nature of the structure. This is the first time in my career where the consequences of something going wrong were such that we can’t afford to take any risks. It is a case of making the quickest job we can. Ultimately it could have been very serious.'

The words of Highways Agency deputy chief executive Derek Turner came back to haunt him today after he described the M4 closure as a ‘hiccup’.

Mr Turner, who earns in excess of £140,000 a year and received a £20,000-plus bonus last year, admitted to reporters when he visited the site on Tuesday that the crack was getting bigger, noting: 'The crack wasn’t there before and was growing, which caused a hiccup in the repair process.’

Today he was believed to be back in the West Midlands as he oversaw the repairs from his Birmingham office 120 miles away.

Delays: As scores of cars get stuck trying to get into London traffic flows smoothly the other way today

Heathrow - 'the gateway to the Games' - is braced for its busiest arrivals day on Monday as teams and officials head for the Olympic village, which also opens that day. Major contingents from Australia and the United States — two of the biggest squads— are due to arrive at the airport tomorrow.

Games organiser Locog said the journey from Heathrow to central London was taking two hours instead of 90 minutes, and only small numbers had arrived so far. Officials who normally use coaches have instead been taken through the congestion by chauffeur-driven BMWs.

Summit: Transport Minister Justine Greening has held emergency talks today to try to solve the problems

White-line painters are on standby to mark out an alternative Olympic-vehicle only route - dubbed ‘Zil lanes’ after the limousines used to ferry communist leaders in specially reserved lanes from the Kremlin during the Soviet era in Russia - which will avoid the M4.

It could run, via Heathrow perimeter roads, from the south side of the airport at Hatton Cross near Terminal 4, to the A30, then to the A4 into central London. Transport for London looks set to make this an official route, which will require it being painted with Olympic rings.

Transport chiefs advised people arriving at the airport to use the Heathrow Express to Paddington or take the Piccadilly line.

Leon Daniels, managing director of surface transport at Transport for London said: ‘We are working closely with the Highways Agency and all Games partners, including LOCOG, to manage traffic flows in London and to welcome athletes and officials to the capital. We will direct traffic onto alternative routes such as the A30/A4 route into central London and manage overall traffic flows as necessary.’

The Highways Agency said there are more than forty workers – split into 14 gangs of between two and four people - working round the clock in three 8-hour shifts repairing the 2 and a half inch crack discovered on Saturday during work which began in March.

A spokesman said: ‘On top of this we have the consulting engineers, technical advisers and welding experts.’

They are fitting four large metal plates to cover the crack, once it has been drilled out and re-filled.

Three of the four metal plates measure 1.5m by 0.75m – or roughly the size of a wardrobe door.

They are 20mm thick and weigh 175kg each – or more than two averagely sized men.

The fourth plate is specially shaped the truss and is 10mm thick and weighs 87kg.

In a humiliating blow to ministers the Agency said the repair work will go on ‘for days’
and will open only ‘when safe to do so.’

Empty: This stretch of the M4 near London was completely closed for emergency maintenance

Cracks: White paint marks the cracks in the elevated section of the Boston Manor Viaduct flyover which need fixing before the Olympics starts. The cracks were first spotted four months ago

It was hoped the work would be completed by Monday which is the busiest day for athletes and VIPs arriving at Heathrow airport for the London 2012 Games – and who will rely on the motorway for entry into London.

The delay will spell embarrassment
for Roads Minister Mike Penning and the Highways Agency. The Agency had
pledged the M4 motorway would be open by rush hour yesterday morning,
though the Minister quickly backtracked and said this would be a ‘hope’.

The Highways Agency confirmed: ‘The
final complex work to repair the Boston Manor Viaduct, just west of
junction 2, has reached a critical stage and, due to the complexity of
the operation, more time than originally envisaged is required to
complete the work safely.

‘As a result, road users are advised the M4 between junctions 2 and 3 in west London will not open on Thursday morning.’

Admission: A post on the Highways Agency website reports the road is expected to re-open from 6.00am on Monday

‘Conditional on the repair work being
successful, it is still expected that the work will be completed and
the road reopened within the next few days.’

The Agency said:’It had been
anticipated this work might be completed by Thursday morning, but we are
in the most sensitive part of the complex repair process and it is
important we get it right, even if that takes more time.

'To do otherwise
would risk the integrity of the whole structure.’

It added:’The Highways Agency and its
contractors are working around the clock and will reopen the motorway
as soon as it is safe to do so.’

More
than half a million motorists have already been hit by the chaos and
that is set to swell to more than a million, costing businesses millions
of pounds in lost orders, appointments and increased congestion.

Determined: Roads minister Mike Penning had vowed the motorway would reopen on schedule

The Highways Agency’s official site says the M4 will remain closed until 6am Monday.

It says: ‘On the M4 eastbound between junctions J4 and J3, there are currently delays of 40 mins caused by congestion due to bridge repairs closing the road between junctions J3 and J2. Road expected to re-open from 6:00 am on 16 July 2012.’

A Highways Agency spokesman said the 6am figure was notional as their traffic computer system required them to put in a set time – but thy hoped to have repairs completed sooner.

But pressed for a time, he said:’ It’s simply the next few days and as soon as possible. We’ll do our best to manage expectations.

'We won’t keep it closed any longer than necessary. We’re working 24 hours round the clock’He said the delay was caused because the repairing the new crack was proving ‘exceptionally complex.’

Four large steel sheets were having now to be put in place to cover the new crack in the bridge support and held in place by 102 metal bolts. They then had to be tested.

This is all on top of the original 1,000 welds which were checked to reveal 64 cracks which needed repair, 57 of which have been completed.

The AA said: ‘Clearly this is a blow to motorists and commuters at a crucial time I the run up to the Olympics.

‘Getting it right is one of the hallmarks of the Olympics. That’s part of the test.

‘But the repairs have to be done properly and safely.’

Drivers planning to travel into west London via the M4 are advised to continue using alternative routes via the M3 or M40.

Roads Minister Mike Penning said: 'I share the frustration of motorists at the continued delay to the opening of the M4.

'However, let’s be absolutely clear,
safety must be paramount and I will not allow the road to be reopened
until this repair work has been completed successfully. This is a very
complex operation and it is not possible to predict precisely how long
it will take.

‘I want to thank motorists for their
patience and assure them that we are doing everything we possibly can to
fix this problem and get the road safely reopened as soon as possible.’

Cracks in the viaduct were discovered
during a planned routine investigation of the structure in March and
repair work has been ongoing.

Repairs are ongoing on the M4 elevated section in west London after cracks were found in the bridge section

Repair job: Road workers are working around the clock to fix the cracked section of the motorway in West London

The Highways Agency said: ‘We took
the decision to close the motorway between junctions 1 and 3 overnight
on Friday.

FRUSTRATED DRIVERS VENT ON TWITTER AS CHAOS CONTINUES

Furious commuters stuck in traffic on the M4 have found one way to fill their time - tweeting about it. But is anyone listening?Here's what they are saying:

Three hours from Ascot to London W6 & two and a half hours back (30 miles each way). That's yer M4 closure

Not looking forward to my first driving shift for Olympics on Monday if M4 still shut.

I swear they need to hurry up and open the M4 again! This traffic is crazy!

M4: Unbearable journeys from and to work last night and this morning... I hate traffic

It took me 2hrs to reach office instead of 40 mins. I would say please avoid M4

M4 is closed. That's not ideal is it.

'I'm very happy they have had to close a stretch of the M4. It gives me the 'opportunity' to waste two extra hours a day in the car ‪#grrrrrr ... Cracks in M4 are causing cracks in my sense of humour.'

'Bearing the brunt of a logistical nightmare regarding the M4 into london!'

'Olympics nearing yet part of M4 is about collapse #WellDone Boris'.

'Hello to everyone struggling in on the M4, M3 and M40 this morning. What a shambles!'

'This was because in entering the final stages of the complex
repair work the Highways Agency found a new crack in a highly stressed
part of the bridge supports.

It said that as a result of the
closure, congestion has increased on other roads in the area and on the
diversion route via the A4 and A312 dual carriageways. Delays of about
15-20 minutes continue to be recorded in both directions for traffic
using the diversion route.

The Agency said:’Congestion has
increased on roads in London which are managed by TfL and local
authorities, with whom the Agency continues to liaise and will make
whatever changes are needed to help keep traffic moving in and out of
London.

‘The indications are that the
measures the Highways Agency was able to implement for Monday morning to
reopen the M4 between junctions 1 and 2 are working to relieve pressure
on the junction 1 (Chiswick) roundabout.’

The M4 is expected to be one of the
busiest routes during the Games because it links the city and Olympic
Park in Stratford with Heathrow.

Professor Stephen Glaister, director
of the RAC Foundation, said: ‘After the queues at Heathrow, now there’s
disruption on the M4. Welcome to Britain.

'The Highways Agency says a crack has
been found at a "sensitive location". Too right it has - on the main
route in and out of the capital for international visitors.

'This raises big question marks about our ability to look after what we already have, let alone provide new infrastructure.'

Labour
is now demanding answers from ministers on the impact of cuts to road
maintenance budgets, which could be the reason for delaying improvement
works until they became crucial.

The party has also raised questions over the readiness of contingency plans for the Olympic and Paralympic Games.

Problem: The road is shut from the Boston Manor Viaduct to Junction 3

John
Woodcock MP, Labour’s Shadow Transport Minister, said: 'It is
astonishing that with less than twenty days to go before the Olympic
Opening Ceremony, a key part of the M4 to Heathrow Airport will be shut
for several days.

'The
Highways Agency has known about issues with the viaduct for at least
four months, so motorway users will be asking why there has been a
panicked closure of the road weeks before the Games.

'Ministers
need to confirm that there are contingency plans in place, so that
another failure of the M4 would not jeopardise the Games. The Tory-led
Government also needs to urgently review the impact of its £435m cuts to
road maintenance budgets and whether they have contributed to this
mess.'

Stuck: The Great West Road (A4) is a key diversion route but has been impassible at times

VIDEO: Video of the chaotic traffic or lack thereof on the M4 as it is closed for repairs...